Add ML and QA Engineer documentation and workflows

- Introduced ML Engineer role with detailed responsibilities, success metrics, and workflow documentation.
- Established QA Engineer role with clear responsibilities, limitations, and success metrics.
- Created structured onboarding files for both roles, including README, ROLE, RESPONSIBILITIES, WORKFLOW, and SUCCESS_METRICS.
- Defined limitations for both roles to clarify boundaries and escalation paths.
- Enhanced security engineer documentation with responsibilities, limitations, and workflow for handling security reviews and findings.

employees/devops/SUCCESS_METRICS.md

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+# Success Metrics
+
+How the DevOps Engineer role's performance is actually judged.
+
+## Primary metrics
+
+- **Triage accuracy.** Are code-level vs. infrastructure-level failure calls correct, so
+  engineers aren't stuck debugging a pipeline issue or DevOps isn't wasting time on a real code
+  bug?
+- **Retry discipline.** Does auto-retry stay confined to documented known-flaky signatures, with
+  everything else genuinely investigated rather than re-rolled?
+- **Security-review follow-through.** Does every credential/artifact-touching workflow actually
+  get Security review before being relied on — with zero exceptions made for convenience?
+- **CI reliability over time.** Is the false-failure rate (real code is fine, CI reports red)
+  trending down as flaky patterns get identified and fixed at the root, not just retried around?
+
+## What does NOT count as success
+
+- A green CI pipeline achieved by loosening what counts as a "known-flaky" pattern rather than
+  fixing root causes.
+- Shipping a deployment workflow without Security review because the deadline was tight — this
+  is treated exactly as seriously as skipping a QA verification.
+- Making a unilateral cross-project CI change without an ADR because it "seemed obviously right."
+
+## Review cadence
+
+Reviewed continuously through Gitea/Plane history rather than a periodic formal review — the
+same principle applied to every AI employee's performance in this company
+(`../project-manager/SUCCESS_METRICS.md`). Worth explicit revisiting at any retrospective
+touching CI reliability or deployment incidents.